The performance of a transmission coupled to an internal combustion engine can be improved by using electrically actuating valves to control transmission torque converters and transmission shifting. For example, a torque converter locking clutch can be slipped at different rates to improve fuel economy and to reduce torque disturbances that a driver may feel when a transmission operates. Further, the pressure of transmission fluid that actuates transmission clutches can be controlled by an electrical actuator so that shift schedules may be varied and so that shift feel may be improved. However, at lower temperatures, frictional losses in electrically operable mechanically actuated valves can increase non-linearly, and additional electrical energy may be needed to operate a valve. As a result, shift feel may degrade and torque disturbances may be more noticeable to a driver. In addition, increased valve resistance can change valve response as well as the complexity of controlling a valve. This may be undesirable since valve performance uniformity is desired over a wide range of operating conditions.
One embodiment of the present description includes a method to improve the performance of an electrically actuated valve operable in a transmission, the method comprising: supplying a time-varying current to at least a coil of an electrically operable mechanical valve actuator that operates a valve of a transmission; said time-varying current increasing eddy currents as a temperature decreases; and said time-varying current decreasing said eddy currents as a temperature increases.
Shift performance can be improved and torque disturbances can be reduced by heating electrically operable mechanically actuated valves. In addition, valve heating can lower valve power consumption and improve valve operation, at least during some conditions by locally decreasing the viscosity of the control fluid. In one embodiment of the present description, a time-varying current may be passed through a coil of an electrically actuated mechanical valve to create a time-varying magnetic field. This field can induce eddy currents in nearby metal components (e.g., in the valve actuator armature and the coil end cap). The eddy currents can be transformed into thermal energy as their flow is restricted by the metal armature. This thermal energy can raise the temperature of transmission fluid that lubricates the actuator armature outer surface, thereby reducing the transmission fluid viscosity. Consequently, the amount of energy necessary to operate the valve can be reduced as the transmission fluid viscosity is lowered. In addition, valve heating can improve valve response and may make a valve respond more predictably.
The present description can provide several advantages. For example, the approach can be used to reduce the amount of power consumed by valves during valve state transitions. Also, the method can allow valves to be heated before an operator requests a vehicle start, which may improve shifting when the transmission is engaged. In addition, valves may be heated in a variety of ways so that a different heating method may be selected based on the geometry of an electrically operable mechanically actuated valve, for example. Further, in some embodiments, heating may be targeted to specific areas of an electrically operable mechanical valve actuator so that energy may be used more efficiently.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.